1. Field of the Invention
The present invention relates to a data recording/reproducing apparatus and method. In particular, the invention relates to a data recording/reproducing apparatus and method for recording/reproducing data using a recording medium such as a DVD (Digital Versatile Disk).
2. Description of Related Art
In recent years, DVDs have been stabilized and come into widespread use. As a standard for recording a video signal or an audio signal on a recording medium such as a DVD (DVD-R, DVD-RW, or DVD-RAM), DVD-Video or DVD+VR (DVD+ReWritable Video format) has been known. The DVD-Video data format is compatible with that the DVD+VR data format. In the following description, the term “DVD-Video standard” refers to not only the DVD-Video and the DVD+VR but also other standards compatible with these in terms of data format.
According to the DVD-Video standards, digital video data or audio data (data stream) which is compression-encoded based on the MPEG2 (Moving Picture Expert Group 2) encoding system is recorded on a DVD.
FIGS. 6A to 6G show a data structure based on the DVD-Video standards. As shown in FIGS. 6A to 6B, data conforming to the DVD-Video standards has a hierarchical structure, and FIG. 6A shows a data structure in the top layer of the hierarchical structure. As shown in FIG. 6A, VMG (Video Manager) is recorded at the head thereof. Following this, up to 99 VTSs (Video Title Sets) are recorded.
As shown in FIG. 6B, VTSI (Video Title Set Information) including control information about a title is recorded at the head of each VTS. Following the VTSI, n VOBSs (Video Object Sets) are recorded.
As shown in FIG. 6C, each VOBS is composed of m VOBs (Video Objects). As shown in FIG. 6D, each VOB is composed of i VOBUs (Video Object Units). Incidentally, according to the DVD-Video standards, the VOB is composed of one or more cells each including n VOBUs.
Here, the DVD-Video and DVD+VR standards specify the maximum number of cells in one VTS as 255. As for the DVD+VR standards, one VOB includes one cell, and one VTS includes up to 255 VOBs. As for the DVD-Video standards, one VOB includes at least one cell, so one VTS includes up to 255 VOBs as well. The number of VOBUs in one VOB varies depending on a bit rate or the number of video frames. The bit rate refers to a data amount of video or audio data per second. The higher bit rate leads to high-quality image and sound.
As shown in FIG. 6E, each VOBU is composed of plural packs, and each pack size is 2,048 bytes. The VOBU includes NV_PCK (Navigation Pack), V_PCK (Video Pack), and A_PCK (Audio Pack) The VOBU may other data such as SP_PCK (Sub Picture Pack). As shown in FIG. 6E, NV_PCK is arranged only at the head of each VOBU. Following the NV_PCK, an arbitrary number of packs such as V_PCK, A_PCK, or SP_PCK are arranged as needed.
In the A_PCK, compression-encoded audio data is recorded, and in the V_PCK, compression-encoded video data is recorded. In the NV_PCK, control information for controlling data in the VOBU such as data about normal reproduction or special reproduction (slow reproduction, high-speed reproduction, and skip reproduction) is recorded. As shown in FIG. 6F, the NV_PCK is composed of a pack header, a system header, DSI packets as retrieval information for retrieving a moving picture or sound to be reproduced/displayed, and PCI packets as display control information for controlling the moving picture or sound retrieved using the DSI packets. As shown in FIG. 6G, the DSI packets include DSI_GI (DSI general information), SML_PBI (seamless reproduction information), SML_AGLI (seamless angle information), VOBU_SRI (VOBU search information), and SYNCI (synchronous information). The SML_PBI includes a reproduction ending time VOB_V_E_PTM, and the VOBU_SRI includes a forward pointer FWDI. In the reproduction ending time VOB_V_E_PTM, every possible ending time of reproduction of all VOBs including the VOBU is recorded. The forward pointer FWDI is forward information, in other words, a pointer for specifying a header address of the VOBU in the VOB, which will be reproduced. In the forward pointer FWDI, header addresses of the second to 241st VOBUs from the viewpoint of a target VOBU (FWDI 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 20, 60, 120, 240) can be recorded.
As mentioned above, data conforming to the DVD-Video standards includes future data such as reproduction ending time VOB_V_E_PTM or forward pointer FWDI. As a result, according to a conventional data recording apparatus, in general, in the case of generating a data stream (video data or audio data, the data stream is temporarily stored in a stream buffer. When the reproduction ending time VOB_V_E_PTM and the forward pointer FWDI are decided, those data are set and recorded on the DVD.
FIG. 7 shows an example of a stream buffer 700 used in the conventional data recording apparatus. The conventional stream buffer 700 sequentially stores data streams generated with an encoder etc. In this example, VOBUs constituting the data stream are stored in order from VOBU#1.
For setting the reproduction ending time VOB_V_E_PTM, the reproduction ending time of the final video frame of the VOB is necessary. Thus, assuming that the VOB is composed of n VOBUs, after the stream buffer 700 stores n VOBUs, the reproduction ending time VOB_V_E_PTM can be set. Accordingly, the stream buffer 700 requires a capacity enough to store all of one VOB.
Further, for setting the forward pointer FWDI, in addition to the setting-target VOBU, VOBUs as many as the forward pointer FWDIs need to be stored in the stream buffer 700. Thus, in the case of setting the forward pointer FWDIs 1 to 240, the stream buffer 700 requires a capacity enough to store 240 or more VOBUs.
Incidentally, as the conventional data recording apparatus, an apparatus as disclosed in Japanese Unexamined Patent Publication No. 2002-56609 has been known. In the apparatus disclosed in Japanese Unexamined Patent Publication No. 2002-56609, the number of VOBUs in the VOB is kept constant, and NV_PCK is previously set based on the number of VOBUs.
As mentioned above, in the conventional data recording apparatus, for setting the reproduction ending time VOB_V_E_PTM or the forward pointer FWDI, the stream buffer should store all VOBUs in one VOB. For example, in the case of recording 255 VOBs on a single DVD, an average size per VOB is about 17 megabytes (=4.2 gigabytes/255), so the stream buffer needs to have a capacity not less than 17 megabytes.
As a result, the conventional data recording apparatus has a problem in that a memory size of the stream buffer is large, and cost reduction of the data recording apparatus is difficult.